1. Field of the Invention
This invention relates to an adjustable pulley construction. It is particularly directed to a pulley construction having adjustable flange members whereby the belt-receiving groove defined by the flange members can be changed, thereby to vary the performance of the pulley.
2. Description of the Prior Art
In an increasing number of applications, relatively high horse power motors are being employed, for example, in applications which require the movement of air, as in industrial heating and cooling systems, relatively large fans are utilized and these required V-belts carry as much as 15 HP. Often the fans will be driven by means of 2-groove variable pitch pulleys. For example, in heating and ventilating applications, a motor of a particular horse power may be designated for use. The output shaft of the motor will ordinarily be utilized for driving a belt which in turn will drive blowers. The performance of the blowers will affect the operating characteristics of the heating and ventilating systems.
Pulleys used for supporting drive belts will determine the blower speeds since the relationship between the diameter of the drive shaft pulley and blower shaft pulley will control the blower shaft speed. In order to permit adjustment of the blower shaft speed to thereby adjust the heating and ventilating operation, adjustable pulleys have been proposed. These pulleys are provided with belt supporting flange members with the spacing between the flange members determining the pitch diameter of the pulley. Thus, if the spacing is increased, the pulley belt will move closer to the pulley axis and, therefore, the pulley will have a smaller effective diameter. By providing pulley constructions which are infinitely adjustable, the heating and ventilating system can be set for most efficient operation.
As capacity requirements increase, the demands on pulley structures have also increased. In many applicaions, belts are required to carry as much as 20 HP and this has led to certain mechanical difficulties where variable pitch pulleys are employed. Usually, such pulleys included a pair of opposing discs, each having an independent hub with the hubs being relatively movable so that the spacing between the pulley discs can be varied. In the usual case, set screws were utilized for securing the hubs of the discs once the desired spacing had been set for a particular application. In some instances, such set screws have, however, been found to be incapable of holding the hubs where high horse powers are involved. In some instances, the common set screw approach has resulted in failure in applications requiring only 71/2 HP per belt.
Another type of usual pulley structure is comprised of a pair of opposed cone dics or pulley halves which cooperate with a V-belt, the variation in effective pitch diameter being obtained by adjusting the axial spacing of the pulley halves on a supporting shaft or sleeve. By moving the pulley halves close together, the belt is caused to move radially outwardly along the conical faces of the pulley halves, thereby producing an increased pitch diameter. When the pulley halves are drawn apart, the belt moves radially inwardly along the faces of the pulley halves to decrease the effective pitch diameter. In drive systems in which the driving and driven pulleys operate on fixed shaft center distances, the driving pulley is customarily provided with a mechanical actuating mechanism for effecting relative movement between the pulley halves.
Although adjustable pulley constructions provide the most effective means for use with heating and ventilating systems, difficulties still characterize such pulleys. The structure thereof is often relatively complex leading to increased costs. Providing adjustable pulley constructions which are securely held on a shaft can also be a problem. Finally the pulley constructions which are adjustable without undue effort are not easily obtained.
Green in U.S. Pat. No. 602,287 patented Apr. 12, 1898 provided a foreshadowing of the basic concept of the adjustable pulley construction with which the present invention is concerned by providing journal-boxes that are used on heavy and fast-running machinery. The box in the patented improvement was so constructed that any wear of either the box or the shaft could be easily and quickly taken up. this construction assured a perfect fit and nice adjustment between the shaft and the journal-box. The construction included an open bushing surrounding the shaft and concentric therewith, in combination with an open eccentric collar fitting inside the journal-box and means for closing said collar around the bushing.
Browning in U.S. Pat. No. 2,010,451 patented Aug. 6, 1935 provided a bushing having shank and flange parts. The bushing shank part had an external keyway, with a key positioned in the keyway and extending into the zone of the bushing flange part, the flange part having an opening receiving the extending key part, the key and bushing having aligned openings radially extending in the zone. Means were arranged in the opening to secure the key against motion along the keyway.
Fuchslocher in U.S. Pat. No. 2,555,189 patented May 29, 1951 provided variable pitch V-pulleys, wherein and whereby the parts of the pulley could be adjusted to and from each other to increase the belt space therebetween, and whereby the parts could be quickly and effectively secured to the shaft on which they were mounted. He provided the combination with a shaft, of an externally threaded bushing, the bushing having a channel formed in its outer side, whereby the wall of the bushing in the bottom of the channel is made thinner, to be flexed. Two pulleys parts, each having a hub portion are threaded on the bushing and are movable toward and from each other thereon by turning on the threads. A setscrew is inserted through each hub portion of the pulley parts and extends into the channel and against the bottom of the channel. Tightening the setscrew flexes the wall into frictional holding engagement with the shaft.
Jackson in U.S. Pat. No. 2,779,202 patented Jan. 29, 1957 provided a multiple sheave for V-belts and the like wherein one or more V-belts could be engaged with a sheave carried on a drive shaft or similar member. The sheave included a plurality of members each comprising a disc-shaped body portion having a center bore and having a peripheral section of frusto-triangular shape in cross-section. A hub portion was provided on one lateral face of the body portion, with the body portion having a set of bores therein parallel to the center bore at equally spaced circumferential portions thereof. The body portion also had a set of tapped holes therein at equally spaced circumferential portions thereof intermediate and of the same size as the set of bores, the set of tapped holes being equal in number to the set of bores. A pair of diametrically opposed keyways were provided in the center bore, with one keyway being spaced circumferentially from an adjacent one of the set of bores the same distance as the other keyway is spaced from the adjacent one of the set of tapped holes.
Trofimov in U.S. Pat. No. 3,491,608 patented Jan. 27, 1970, provided an adjustable pulley having a control shaft which was supported in an improved manner against axial deflection with respect to an inner shaft or sleeve on which the fixed pulley face was mounted. The movable pulley face had an elongated hub slidable on the inner sleeve or shaft and an outboard end supported by the control shaft. The mounting of the control shaft prevented axial deflection thereof and assured that the various parts of the pulley, including the inner shaft or sleeve, the movable pulley face and the control shaft, would be coaxial and would run true during use so as to minimize or eliminate misalignment and uneven wear of the drive belt. Further, the outboard end of the movable pulley face was supported in such a manner as to minimize the loading on the bearings, thereby improving the life of the pulley. The pulley could be relatively easily and inexpensively manufactured because of the fact that the tolerance requirements, particularly of the bearings and the bearing supporting surfaces, were said to be not as great as in conventional constructions.
Firth in U.S. Pat. No. 3,680,404 patented Aug. 1, 1972 provided a variable pitch sheave which was formed of two discs each having a belt-contacting surface and a hub. The hubs had screw threaded interfit, with the threads of the inner hub being interrupted by at least one abutment surface, and the other hub having at least one radial screw threaded bore to receive a set screw to press against an abutment surface of the inner hub. The inner hub was split at two points spaced from the abutment surface, and its disc was split on one radius only thereof. Tightening of the set screw when the discs were in selected laterally spaced relation while the inner hub was mounted on a shaft, served the dual purpose of preventing relative rotation of the hubs to maintain the selected spacing of the disc and of clamping the inner hub upon the shaft.
Maurey in U.S. Pat. No. 3,661,023 patented May 9, 1972 provided an adjustable pulley construction comprising a pair of discs each having a centrally located hub and defining opposed belt engaging surfaces. The hubs were threaded or otherwise designed for relative axial movement whereby the distance between the belt engaging surfaces could be adjusted. Means were provided for securing the hubs together including a set screw located in a threaded bore defined by the exterior hub. The set screw defined a tapered end which was received within a tapered opening formed in a key located in line with the threaded bore. This key was inserted between the end of the bore and the surface of the inner hub. As the set screw was rotated, the degree of pressure applied by the key on the inner hub could be adjusted whereby an extremely secure relationship between the hubs was said to be achieved.
Maurey in U.S. Pat. No. 3,815,432 patented June 11, 1974 provided a pulley construction wherein a pair of flange members were mounted on a shaft, and wherein the hub of one flange member was received within the hub of the other flange member. The flange members were adjustably secured on the shaft whereby the size of the belt receiving groove between the flange members could be changed. The securing means took the form of a wedge defining side edges, and channels which were defined in the hub for receiving the wedge. A set screw was receivable within an opening defined by one hub and within an aligned opening defined by the wedge. The wedge was preferably split so that movement of the set screw within the wedge opening operated to drive the wedge sections into engagement with the adjacent channel faces thereby tying the hubs together. A separate opening could be provided in either hub for receiving a set screw which served to tie the assembly of flange members against movement relative to the shaft.
Thus, the hereinabove described conventional adjustable control pulleys generally took the form of a movable pulley face having a sleeve-type bushing usually made of metal and/or plastic fixed in its hub which is axially slidable on a hollow metal shaft toward and away from a fixed pulley face. A control rod or shaft had one end rotatably supported within the hollow shaft by either a single or a two-row type ball bearing. The control rod projected from the hollow shaft and was threadedly connected to the movable pulley face so that it could be adjustably positioned relative to the fixed pulley face.
Deficiencies of the Prior Art
The foregoing pulley construction of the prior art is relatively difficult to manufacture, since the sleeve-type bushing, the inner surface of the hub of the movable pulley face and the hollow supporting shaft must be carefully formed to close dimensional tolerances in order that the control shaft will be concentric in the hollow shaft and will run true in the single or two-row ball bearing. During operation of such a pulley, the drive belt exerts a cocking force on the movable pulley face. If the movable pulley face is somewhat loose on the hollow supporting shaft, either because of machining inaccuracies or simply because of bushing wear, the cocking force will be transmitted to the control shaft causing it to deflect axially and to be misaligned in the ball bearing, thereby resulting in overheating of the bearing and premature failure. Furthermore, when the pulleys were disposed in a vertical orientation there was danger of accidental disassembly should a set screw become loosened.